1. Field of the Invention
The present invention relates to a welded tube with an excellent corrosion-resistant inner surface, in which the inner surface as plated with a metal or alloy has excellent corrosion resistance to be free from corrosion especially that from the welded part (hereinafter referred to as a bead part) and also to a method of producing the same.
2. Description of the Prior Arts
Heretofore, a small-diameter steel tube has been used as a fuel pipe for cars. As pipes for lower gasoline, sour gasoline, alcohol and alcohol-mixed fuels, formation of an anti-rusting metal layer on the inner surface thereof for improving the rust resistance of it has been proposed. For instance, there has been used a welded steel tube with improved inner surface rusting resistance to be produced by a method in which at least one surface of a steel strip is plated with nickel by electric plating, the thus plated strip is formed into a tube by roll forming with the plated inner surface being inside, the butt joint area of the rolled tube is welded by electric resistance welding with electrode rolls or the like and the tube is finally annealed.
However, since the welded tube of the kind having a nickel plate layer on the inner surface thereof is produced by welding the butt joint area thereof by electric resistance welding or the like after the roll forming, the bead part to be formed on the inner surface of the tube often has discontinuous areas also in the nickel plate layer thereon to cause local exposure of the steel base out of the plate layer (see FIG. 2), or as the case may be, pin holes existing in the nickel plate layer in the part would often remain as they are. As a result, the part involves a problem that it would easily be corroded by water to be in alcohol or alcohol-mixed fuel or by organic acids to be formed by oxidation of gasoline or decomposition of alcohol.